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        .rela_1em p,.rela_1em ul li{
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    <h2>相对长度(1em=12px)</h2>
    <div class="rela_1em">
        <h3>1em</h3>
        <p>You can! But maybe you shouldn't. This is an interesting consequence of a bunch of hacks held together with
            duct tape. It uses z-index hacks, gradient hacks and tricks with calc and viewport units.
        </p>
        <p>You can! But maybe you shouldn't. This is an interesting consequence of a bunch of hacks held together with
            duct tape. It uses z-index hacks, gradient hacks and tricks with calc and viewport units.
        </p>
        <p>Having said that, hacks are not always bad. I love hacks and many of us have made quite a good living selling
            floats and clearfixes.
        </p>
        <ul>
            <li>Ullamcorper Aenean Ornare</li>
            <li>Ridiculus Lorem Malesuada Consectetur</li>
            <li>Aenean Tristique Sit Lorem Purus</li>
            <li>Vehicula Egestas Mollis Cursus Nibh</li>
        </ul>
    </div>
    <div class="rela_2em">
        <h3>2em</h3>
        <p>You can! But maybe you shouldn't. This is an interesting consequence of a bunch of hacks held together with
            duct tape. It uses z-index hacks, gradient hacks and tricks with calc and viewport units.
        </p>
        <p>You can! But maybe you shouldn't. This is an interesting consequence of a bunch of hacks held together with
            duct tape. It uses z-index hacks, gradient hacks and tricks with calc and viewport units.
        </p>
        <p>Having said that, hacks are not always bad. I love hacks and many of us have made quite a good living selling
            floats and clearfixes.
        </p>
        <ul>
            <li>Ullamcorper Aenean Ornare</li>
            <li>Ridiculus Lorem Malesuada Consectetur</li>
            <li>Aenean Tristique Sit Lorem Purus</li>
            <li>Vehicula Egestas Mollis Cursus Nibh</li>
        </ul>
    </div>
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